JEE Main & Advanced Physics Wave Optics / तरंग प्रकाशिकी Question Bank Doppler's Effect of Light

  • question_answer
    The observed wavelength of light coming from a distant galaxy is found to be increased by 0.5% as compared with that coming from a terrestrial source. The galaxy is [MP PMT 1993, 2003]

    A)            Stationary with respect to the earth

    B)            Approaching the earth with velocity of light

    C)            Receding from the earth with the velocity of light

    D)            Receding from the earth with a velocity equal to \[1.5\times {{10}^{6}}m/s\]

    Correct Answer: D

    Solution :

                       \[\frac{\Delta \lambda }{\lambda }=\frac{v}{c},\]Now \[\Delta \lambda =\frac{0.5}{100}\lambda \Rightarrow \frac{\Delta \lambda }{\lambda }=\frac{0.5}{100}\]                    \[\therefore v=\frac{0.5}{100}\times c=\frac{0.5}{100}\times 3\times {{10}^{8}}=1.5\times {{10}^{6}}m/s\]            Increase in l indicates that the star is receding.


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